Fix race between chain and keys services when starting with persisted chain
Fix race between chain and keys services when starting with persisted chain

Start process responsible for keys (`aec_keys`) first because it is
used by (at least):

* Chain process (`aec_chain`/`aec_chain_server` - see module
  `aec_chain_state`);

* Mempool process (`aec_tx_pool`).

In particular, chain process needs keys process when loading persisted
chain.

Thanks to Dimitar for reproducing issue (PT-152793276), and Dimitar
and Ulf for proposing fix.

aeternity/epoch,aeternity/epoch,aeternity/epoch,aeternity/epoch